In recent image forming apparatuses of this type, a belt fixing method that allows setting of a low heat capacity has attracted attention in response to requests for reduction of warm-up time (a period from when the image forming apparatus is powered on to when a fixing device becomes ready to perform fixing) and energy saving in the fixing device. Also, an electromagnetic induction heating (IH) method capable of rapid heating and high-efficiency heating has attracted attention as a heating method adopted in the fixing device. From the viewpoint of energy saving in fixing of a color image, a large number of fixing devices utilizing the electromagnetic induction heating method and the belt fixing method in combination have been commercialized.
More specifically, a structure in which a coil for generating magnetic flux for electromagnetic induction is provided on the outside of a belt (so-called external IH) has been proposed in the electromagnetic induction heating method. In an electromagnetic induction heating apparatus that adopts the external IH, a coil is mounted on a coil bobbin. Further, a ferrite core portion is provided opposite to a heat roller with the coil and the coil bobbin sandwiched therebetween so as to form a magnetic path around the coil.
The above-described ferrite core portion is fixed to resin members, such as the coil bobbin on the inner side of the core portion and a core holder on the outer side of the core portion, with an adhesive such as a heat-resistant silicone adhesive. A layer of such an adhesive for fixing the core portion is resistant to high temperature during induction heating, and has the function of absorbing (e.g., compensating for or accommodating) production dimensional variation in the core portion. More specifically, the adhesive layer can absorb dimensional variation due to contraction caused when powder is pressed and sintered to form the core portion. Further, the adhesive layer can reduce vibration noise (chattering noise) from the core portion due to resonance of the core portion with high-frequency magnetic flux produced in the coil.
Nevertheless, as recognized by the present inventor, fixing with the adhesive is associated with various problems in production efficiency of the fixing device. For instance, the operation of applying the adhesive onto the coil bobbin and the core holder is itself inefficient. Moreover, some time is required for the adhesive to set, and space is required for storing the components with the adhesive applied thereon until the adhesive sets. The related art, however, does not particularly consider any solution to these problems.